Conventionally, in a fluid piping system having a gas meter instrument, as a gas meter instrument for identifying an appliance being used, an instrument described in Patent document 1 is available. Its configuration will be described referring to FIG. 12. FIG. 12 is a block diagram showing a conventional gas meter.
As shown in FIG. 12, a gas meter instrument 1 is disposed in a flow passage 6 connected to a household gas supply pipe and is equipped with a flow rate measurement unit 3 for measuring the flow rate of gas at constant time intervals; a calculation unit 4 for obtaining the difference values of flow rate values output from the flow rate measurement unit 3; and a comparison judgment unit 7 for comparing the difference values calculated by the calculation unit 4 with a change judgment value registered in a storage unit 5 and for judging the change of the usage state of a gas appliance. The calculation unit 4, the comparison judgment unit 7 and a gas shut-off valve 2 are controlled by a control circuit 116.
The above-mentioned gas meter instrument 1 sequentially calculates the change of the difference values of the instantaneous flow rate output from the flow rate measurement unit 3 and judges the change of the usage state of the gas appliance according to the amount of the change, wherein registered data is compared with the change (difference values) of the gas flow rate measured, whereby the identification of gas appliances 13, 14 and 15 is made possible.
Furthermore, as a conventional method for identifying an appliance that uses fluid, a method described in Patent document 2 is available. Its configuration will be described referring to FIG. 13. FIG. 13 is a block diagram showing a conventional flow rate measuring device.
As shown in FIG. 13, a calculation unit 108 calculates the difference values of the gas flow rate measured by an ultrasonic flowmeter 104 at constant time intervals and a difference value conversion unit 112 classifies the difference values obtained at constant time intervals into predetermined classifications using the flow rate classification table 110a stored in a flow rate classification table storage unit 110 and converts the classifications into predetermined codes. An appliance identification unit 116 compares the code string generated by a code string generation unit 114 using the codes converted by the difference value conversion unit 112 with an appliance inherent feature code string being inherent in each appliance and stored in an appliance inherent code string information storage unit 118 to perform appliance identification.
In the above-mentioned configuration, code values obtained by coding (converting) the difference values of the flow rate are used, and the calculation is simplified when appliance identification is performed, whereby the speed of the calculation and the accuracy of the appliance identification are improved while the amount of memory required for the calculation, for example, is reduced.    Patent document 1: Japanese Patent Application Laid-Open Publication No. 2006-313114    Patent document 2: Japanese Patent Application Laid-Open Publication No. 2008-309498